Optical masers or lasers, as the art has developed, generally involve the establishment of an artificial distribution of bound electrons at energy levels other than the natural distribution in a host environment through the application of a source of energy known as the "pumping energy." This results in a greater number of molecules or atoms in some high energy level than in a lower energy level to which it is optically connected. This is known as a population inversion. The electrons present in the host environment in the artificial distribution then give up their energy and undergo a transition to the lower energy level. The released energy may be in the form of electromagnetic radiation; which, in the majority of devices seen thus far in the art, has been light, either in the visible or infrared.
In laser devices currently available in the art, there may be employed a gas, such as a helium-neon mixture; or a crystal, such as chromium doped aluminum oxide; or a non-crystalline solid, such as neodymium glass; or a liquid, such as trivalent neodymium in selenium oxychloride, as the environment which responds to the pumping energy, permitting the population inversion of electrons between an excited state and a lower state. The electrons in returning to the lower state give off quanta of light energy or photons in what is known in the art as a radiative transition. When the density of these photons becomes large, the radiative transition probability increases; and, in the presence of a population inversion, electromagnetic modes into which the photons are emitted, in turn, become most readily able to induce further emission therein. This is known in the art as stimulated emission of radiation and results in a narrowing of the emission line. In the currently available laser devices, electrical power is converted to optical power, pumping light or an electrical discharge or electric current; which, in turn, is used to establish the population inversion. All known prior art lasers are of relatively low power. A high power laser has been a long sought need for a large number of potential applications, both military and commercial, and numerous, attempts have been made to provide a truly high power laser. The gas laser is the general category into which most of these efforts have fitted.
In the Polanyi references identified hereinafter, it is suggested that total and partial inversions may be obtained as a direct result of chemical reaction. Without flow, such inversions are transient. Even if the gas is pulsed thermally and permitted to relax differentially, such disclosed devices are inherently low density devices since the translational and rotational energy is removed by diffusion to the walls. The Hurle et al paper also identified hereinafter suggests supersonic expansion as a method of producing population inversion between electronic states by differential radiation relaxation. While presumably in theory (Hurle et al admit that they were unable to observe an inversion) an inverted population can be produced in this fashion, the size of a device based solely on this principle is limited because of radiative trapping and also the stagnation temperatures required to have a significant fraction of the energy in the desired electronic level at equilibrium are quite high.
The following references and materials cited therein describe some of the background and physical principles involved in the devices under discussion and an insight, to some degree, of application of those principles in the present state of the art:
1. "Infrared and Optical Masers," by A. L. Shawlow and C. H. Townes in Physical Review, Vol. 112, Np. 6, Dec. 15, 1958, pp 1940-1949. PA1 2. "Attainment of Negative Temperatures by Heating and Cooling of a System" by N. G. Basov and A. N. Oraevskii, Soviet Physics JETP, Vol. 17, No. 5, Nov. 1963, pp 1171-1172. PA1 3. "Population Inversion in Adiabatic Expansion of a Gas Mixture" by V. K. Konyukhov and A. M. Prokhorov, JETP Letters, Vol. 3, No. 11, 1 June 1966, pp 286-288. PA1 4. "Electronic Population Inversions by Fluid-Mechanical Techniques" by I. R. Hurle and A. Hertzberg, The Physics of Fluids, Vol. 8, No. 9, Sept. 1965, pp 1601-1607. PA1 5. Polanyi, J. C., J. Chem. Phys. 34, 347 (1961). PA1 6. Polanyi, J. C., Applied Optics Supplement No. 2 on Chemical Lasers, 109 (1965).